I said it was a completely useless way to practice improv, and it is.

You don't get better at improvising by running scales and arpeggios all day, you just get really good at playing scales and arpeggios.

Here's my problem with scale/arpeggio based practice as it applies to playing actual music. Even though you might be practicing to a metronome you've removed the most important part of playing a tune, the temporal element, i.e. the chord changes and placement of notes in the bar.

Every scale player I've ever taught had the same problems, they'd get lost in the tune because they weren't hearing what they're playing and they would lack the ability to spell out the changes by landing chord tones on strong beats and no ability to decorate the diatonic scale they were totally reliant on.

Essentially they were running scales and arpeggios without any ability to actually use them to make cohesive musical ideas.

I'm not saying you don't need to know scales/arpeggios, of course you do but that is not even half the battle. Learning how to apply them to a chord and, more importantly, how to align them to the bar is the more difficult and more important aspect.

People will often tell you to spend hours running scales in every key, in every position etc. but that is, imo, a total waste of practice time.

If you want to practice a scale, do it in the context of a tune while applying it to moving chord changes and work on hitting chord tones on strong beats.

My advice on how to best improve your improv, if you are struggling is to take a simple progression like a ii V I, loop record yourself playing it and play along.

Now, starting with the ii, pick a chord tone, i.e. root, 3rd, 5th or 7th play it on beat 1 and hold it for the whole bar. When the chord changes move to the nearest chord tone of that chord and, again, just play one note for the whole bar.

Once the progression has cycled pick another chord tone to start with and go around again, one note per bar.

From here you can progress to playing two notes per bar, one beats 1 and 3, both chord tones and, again, move to the nearest chord tone of the next chord when it changes.

Now start decorating your chord tones with scale tones and chromatic notes. You can use chromatic neighbor tones to approach your chord tones, one, two or three scale-wise approach notes, either ascending or descending and diatonic or chromatic enclosures to embellish the melody, keeping the chord tones on beats one and three at all times.

Eventually you can build up to a running 8th note line use all combinations of those decoration techniques.

The key thing is to get the sound of them in your head, the object is to be "hearing" them as you play rather than thinking solely about scales.